1. Field of the Invention
The present invention relates to a solid electrolytic capacitor.
2. Description of the Prior Art
A solid electrolytic capacitor has a structure in which an anode is formed of a valve metal such as aluminum, tantalum, niobium, or the like; an oxide film as a dielectric layer is formed by anodizing the anode; and a solid electrolytic layer and a cathode layer are laminated on the dielectric layer in this order.
In recent years, with the demand for digitalization of a circuit and miniaturization of electronic equipment, there is an increasing demand for high-frequency response characteristics and miniaturization of electronic components. Also in a solid electrolytic capacitor, in order to meet such demands, low resistance of a conductor part such as a solid electrolytic layer, a cathode layer, and the like and miniaturization and large capacitance of a solid electrolytic capacitor is promoted.
For realizing miniaturization and large capacitance of a solid electrolytic capacitor, a laminated type solid electrolytic capacitor in which a plurality of capacitor units are laminated is proposed. FIG. 13A is a perspective view of a conventional solid electrolytic capacitor, and FIG. 13B is a cross-sectional view taken along line Ixe2x80x94I in FIG. 13A. In general, the electrolytic capacitor is produced as follows. First, a capacitor unit is formed by forming a dielectric layer 2, a solid electrolytic layer 3 and a cathode layer 4 in this order on the predetermined surface of an anode layer 1. Then, a plurality of capacitor units are laminated via a conductive adhesive 5 to form a unit laminate. Next, the anode lead portions 1a that are not covered with a solid electrolytic layer and the like are bundled and integrated into an anodic extraction terminal 13 by welding. Furthermore, a cathodic extraction terminal 9 is connected to a cathode layer 4 of the capacitor unit constituting the bottom layer of the laminate via a conductive adhesive 7. Finally, a sealing body 8 is formed in a state in which the anodic extraction terminal 13 and the cathodic extraction terminal 9 are exposed to the outside.
In a solid electrolytic capacitor, further miniaturization and large capacitance are demanded. At the same time, in order to improve the high-frequency response characteristics of the products, the connection between conductors, in particular the connection between a valve metal as an anode and an anodic terminal, has further been demanded to have low resistance property and improved reliability.
JP 6 (1994)-84716 A discloses a method in which an anode of each capacitor unit is exposed to the outside of the sealing body respectively; a conductive layer formed of a thermal spraying layer, a sputtering film, a conductive resin, or the like is formed so as to cover the exposed portion; and anodes are electrically integrated via the conductive layer. According to this method, since the space necessary to integrate the anodes becomes smaller as compared with the capacitor shown in FIGS. 13A and 13B, it is possible to achieve further miniaturization and large capacitance. However, since an interface resistance between the anode and the conductive layer due to a natural oxide film formed on the surface of the valve metal is large, there are disadvantages in that connection with low resistance and high reliability cannot be obtained.
Furthermore, JP 8 (1996)-273983 A describes a method of forming a metal plating layer on the surface of each anode layer and connecting this respective metal plating layer to a further plating layer; and a method of connecting the individual metal plating layers to each other by soldering or welding. However, in the former method in which the anodes are connected to each other only by a plating layer, there is a problem in the reliability of the mechanical strength, etc. Furthermore, in a latter method in which a plating layer is connected by welding and the like, a thermal effect due to high temperature heating in welding is not negligible, thus deteriorating the quality of products. In addition, since the plating layer is generally thin, there is an industrial difficulty in connecting the extremely thin plating layers to each other by welding, that is, by fusing of metals.
Therefore, with the foregoing in mind, it is an object of the present invention to provide a solid electrolytic capacitor realizing miniaturization and large capacitance and capable of obtaining a low resistance and high reliability when electrically connecting anodes to each other.
In order to achieve the above-mentioned object, the first solid electrolytic capacitor of the present invention includes a laminate comprising a plurality of capacitor units, each capacitor unit comprising an anode made of a valve metal, a dielectric layer formed on the anode and a solid electrolytic layer formed on the dielectric layer; a sealing body for sealing the laminate; and an anodic conductive elastic body formed outside the sealing body and electrically connected to the anode; the anodes being electrically connected to each other via the anodic conductive elastic body; wherein a part of the anode is exposed to the outside of the sealing body, and the exposed portion of the anode is covered with a plating layer and electrically connected to the anodic conductive elastic body via the plating layer.
With such a configuration, since the space necessary for electric integration of the anodes can be reduced, it is possible to realize miniaturization and large capacitance of a solid electrolytic capacitor. Furthermore, since a plating layer is interposed between the anode and the anodic conductive elastic body, it is possible to suppress the increase of the interface resistance between the anode and the conductive elastic body due to a natural oxide film formed on the surface of the valve metal, and thus to realize the connection with low resistance and high reliability.
It is preferable that the first solid electrolytic capacitor further includes a cathode layer being laminated on the solid electrolytic layer.
Furthermore, the second solid electrolytic capacitor of the present invention includes a laminate comprising a plurality of capacitor units, each capacitor unit comprising an anode made of a valve metal, a dielectric layer formed on the anode, a solid electrolytic layer formed on the dielectric layer and a cathode layer formed on the solid electrolytic layer; a sealing body for sealing the laminate; and an anodic conductive elastic body formed outside the sealing body and electrically connected to the anode; the anodes being electrically connected to each other via the anodic conductive elastic body; wherein a part of the anode is exposed to the outside of the sealing body, and the exposed portion of the anode is covered with a plating layer and electrically connected to the anodic conductive elastic body via the plating layer.
With such a configuration, since the space necessary for electric integration of the anodes can be reduced, it is possible to achieve miniaturization and large capacitance of a solid electrolytic capacitor. Furthermore, since a plating layer is interposed between the anode and the anodic conductive elastic body, it is possible to suppress the increase of the interface resistance between the anode and the conductive elastic body due to a natural oxide film formed on the surface of the valve metal, and thus to realize the connection with low resistance and high reliability.
Furthermore, in the first and second solid electrolytic capacitors, it is preferable that the plating layer has a multi-layer structure. For example, by constituting the plating layer by a plurality of plating layers having a various kinds of materials, it is possible to compensate for respective defects in the properties of each plating material.
Furthermore, in the solid electrolytic capacitor, the plating layer includes at least one selected from the group consisting of a nickel plating layer, a copper plating layer, a zinc plating layer, a silver plating layer, a tin plating layer, a gold plating layer and a solder plating layer. Nickel plating herein is defined as a plating including nickel as a main component. This definition applies to the other kinds of metal plating. The main component herein denotes a component with the largest content (wt. %) in the plating.
Furthermore, in the first and second solid electrolytic capacitors, it is preferable that the anodic conductive elastic body is formed of a resin comprising conductive powder.
Furthermore, in the first and second solid electrolytic capacitors, it is preferable that the conductive powder is at least one selected from the group consisting of silver powder, copper powder, and carbon powder. This is preferable because the conductive powder has high conductivity, and thus resistance can be lowered further.
Furthermore, it is preferable that the first and second solid electrolytic capacitors further include a metal electrode formed outside the sealing body and electrically connected to the anodic conductive elastic body. This is preferable because resistance can be lowered further.
Furthermore, in the first and second solid electrolytic capacitors, as the metal electrode, a metal plate or metal cap can be used. In this case, a part in which the metal plate or metal cap is in contact with the anodic conductive elastic body is plated. As the plating layer, for example, silver plating layer and gold plating layer are preferred for realizing the low resistance property. Furthermore, it is preferable that the above-mentioned plating layer has a multi-layer structure. For example, by constituting the plating layer of a plurality of plating layers having various kinds of materials, it is possible to compensate for respective defects in properties of each plating material. Furthermore, as the metal electrode, a metal layer formed by plating can be used.
Furthermore, in the first and second solid electrolytic capacitors, it is preferable that the capacitor units are laminated to each other via a conductive adhesive and the solid electrolytic layers are electrically connected to each other via this conductive adhesive.
Furthermore, it is preferable that the first and second solid electrolytic capacitors further comprising a cathodic terminal electrically connected to the solid electrolytic layer and the cathodic terminal are adjacent to all the capacitor units constituting the laminate and directly connected to all the capacitor units via a conductive adhesive. This is preferable because it is possible to extract capacitance from each capacitor unit with low resistance easily and to obtain a capacitor with excellent high-frequency response characteristics.
In this case, as the cathodic terminal, a lead frame can be used and a part of the lead frame is exposed to the outside of the sealing body.
Furthermore, as the cathodic terminal, a metal chip can be used and a part of the metal chip is exposed to the outside of the sealing body. It is preferable that as the metal chip, a metal including at least one of silver and gold is used.
Furthermore, in the first and second solid electrolytic capacitors, it is preferable that a part of the metal chip exposed to the outside of the sealing body is covered with a cathodic conductive elastic body. Furthermore, it is preferable that the first and second solid electrolytic capacitors include a metal electrode that is electrically connected to the cathodic conductive elastic body.
Furthermore, in the first and second solid electrolytic capacitors, it is preferable that the capacitor units are laminated to each other via a metal foil and the solid electrolytic layers are electrically connected to each other via this metal foil.
In this case, it is preferable that the metal foil is formed of the valve metal. Furthermore, it is preferable that the first and second solid electrolytic capacitors further include a cathodic conductive elastic body formed outside the sealing body and electrically connected to the metal foil, wherein a part of the metal foil is exposed to the outside of the sealing body and the exposed portion is covered with the plating layer and electrically connected to the cathodic conductive elastic body via the plating layer. Furthermore, it is preferable that the metal electrode formed outside the sealing body and electrically connected to the cathodic conductive elastic layer is included.
As the cathodic conductive elastic body, a resin including conductive powder is preferably used. Furthermore, it is preferable that the conductive powder is at least one selected from the group consisting of silver powder, copper powder, and carbon powder.
As the metal electrode, it is possible to use a metal plate or metal cap. In this case, a part in which the metal plate or metal cap is in contact with the cathodic conductive elastic body is plated. As the plating layer, for example, a silver plating layer and gold plating layer are preferred for realizing the low resistance property. Furthermore, it is preferable that the above-mentioned plating layer has a multi-layer structure. For example, by constituting the plating layer of a plurality of plating layers having various kinds of materials, it is possible to compensate for respective defects in properties of each plating material. Furthermore, as the metal electrode, a metal layer formed by plating can be used.